CVE-2023-40548: A buffer overflow was found in Shim in the 32-bit system

Q: How do I fix CVE-2023-40548?

shim: upgrade to 15.8; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2023-40548 being exploited?

CVE-2023-40548 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2023-40548 affect?

CVE-2023-40548 affects shim, fedora. Severity is high (CVSS 7.4). A buffer overflow was found in Shim in the 32-bit system. The overflow happens due to an addition operation involving a user-controlled value parsed from the PE binary being used by Shim. This value is further used for memory allocation ope

Q: How urgent is CVE-2023-40548?

Priority 40/100. High severity; On your watchlist

This month

HIGH 7.4WATCHLISTUPGRADEMITIGATE

CVE-2023-40548 is a high-severity flaw (CVSS 7.4) affecting shim, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A buffer overflow was found in Shim in the 32-bit system. The overflow happens due to an addition operation involving a user-controlled value parsed from the PE binary being used by Shim. This value is further used for memory allocation operations, leading to a heap-based buffer overflow. This flaw causes memory corruption and can lead to a crash or data integrity issues during the boot phase.

Why this priority

High severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.4 (High)
Attack vector	Local
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-190, CWE-787
Published	2024-01-29
Last modified	2026-06-26

Publisher (CNA): Red Hat, Inc. · Vendor: fedoraproject · redhat

Last updated 2026-06-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2024-01-29 15:15 UTCPublished CVE record published
2026-06-26 10:16 UTCUpdated Record last modified

redhat shim UPGRADE

Affected: < 15.8 · 15.8 rc1

Fixed in: 15.8

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy shim || rpm -q shim || shim --version

2. UPGRADE to 15.8 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade shim

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade shim

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

fedoraproject fedora MITIGATE

Affected: 39

Fixed in: no fixed release known

Safe to downgrade to: a release before 39

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2023-40548?

shim: upgrade to 15.8; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2023-40548 being exploited?

CVE-2023-40548 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2023-40548 affect?

CVE-2023-40548 affects shim, fedora. Severity is high (CVSS 7.4). A buffer overflow was found in Shim in the 32-bit system. The overflow happens due to an addition operation involving a user-controlled value parsed from the PE binary being used by Shim. This value is further used for memory allocation ope

How urgent is CVE-2023-40548?

Priority 40/100. High severity; On your watchlist

Related CVEs

CVE-2023-40547 HIGH 8.3 UPGRADE MITIGATE A remote code execution vulnerability was found in Shim
CVE-2023-40551 MEDIUM 5.1 UPGRADE MITIGATE A flaw was found in the MZ binary format in Shim
CVE-2023-40550 MEDIUM 5.5 UPGRADE MITIGATE An out-of-bounds read flaw was found in Shim when it tried to validate the SBAT information
CVE-2023-40549 MEDIUM 6.2 UPGRADE MITIGATE An out-of-bounds read flaw was found in Shim due to the lack of proper boundary verification during the load o
CVE-2023-40546 MEDIUM 6.2 UPGRADE MITIGATE A flaw was found in Shim when an error happened while creating a new ESL variable

References

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